Conventionally, a thermal-type air flow measuring device for measuring an air flow rate by use of heat transfer from a heating element to a flow of air is widely known. This air flow measuring device is employed, for example, for measuring a flow rate of intake air taken into an internal combustion engine. In the air flow measuring device, a sensing part is configured by disposing an element such as a heating element on a semiconductor substrate in the light of improvement in responsivity and improvement in measurement accuracy. The air flow measuring device is obtained by inserting a subassy holding this sensing part into a housing, which defines a passage of air.
The housing of the air flow measuring device is a hollow body made of resin and having a hollow portion, and the hollow portion is used as, for example, the passage of air. For this reason, the housing is obtained for example, by injection-molding components made of resin for forming the hollow portion, and then, by joining together the respective resin components through adhesive bonding (see, for example, JP-A-H11-258019 and JP-A-2006-234766). However, the adhesive may protrude into the hollow portion, and the flow of air in the hollow portion may be disturbed due to the protruded adhesive.
For a method for making the resin hollow body, in addition to the joining method through the adhesive, a method referred to as a die slide injection molding (abbreviated as DSI) method is widely known (see, for example, Japanese Patent No. 3263167).
The DSI method includes, for example, a primary formation process in which resin components defining a hollow portion (hereinafter referred to as half hollow bodies) are formed through injection-molding; a die moving process in which with the respective half hollow bodies held in dies used in the primary formation process, joining edges of the half hollow bodies are brought close to each other by movements of dies relative to each other to give the half hollow bodies a predetermined arrangement; and a secondary formation process in which molten resin is injected into a region where the joining edges of the half hollow bodies are adjacent to each other, and the joining edges are joined together.
As a result of these processes, according to the DSI method, the half hollow bodies which are injection-molded in the primary formation process can quickly be joined together in the secondary formation process before, for example, warping deformation after the formation is caused. Accordingly, by using the DSI method for the method of making the housing of the air flow measuring device, problems caused by the protrusion of the adhesive can be solved, and reduction of manufacturing man hours, quality improvement in joining portions and so forth can be achieved.
When a flow rate of air with pulsation is measured by the thermal-type air flow measuring device, a negative-side measurement error, whereby the measured value becomes lower than a true value because the measuring method is of the thermal type, is caused. For this reason, to reduce the negative-side measurement error as a result of the measurement of pulsation, it is necessary that a passage in the housing be formed so as to have a curved part and the sensing part project into the passage. Accordingly, the resin hollow body as a housing includes a partition wall that projects into the hollow portion to divide the hollow portion, in addition to an outer wall that divides the hollow portion from the outside of the body. The curved part of the passage is defined by the partition wall.
Since the partition wall is provided by the joining or contact of the joining edges, if, for example, a joining at the partition wall, is insufficient, a leakage of air at the partition wall is caused. As a result, a part of air introduced into the housing does not pass through the curved part and takes a shortcut, which has an adverse effect on the measurement. Therefore, when the DSI method is employed as a production method of the housing, reliability of prevention against an air leak at the partition wall needs to be enhanced.